Progress of CO2 Electrochemical Methanation Using a Membrane Electrode Assembly

CO₂ reduction and fixation are one of the most interesting topics in the fields of environmental electrochemistry and electrocatalysis. Many studies on CO₂ electroreduction using various metal electrodes have been reported. However, this reaction requires a high overpotential in general, which lowers the energy conversion efficiency and prevents its practical applications to reduce CO₂ emission to the atmosphere. The use of a membrane electrode assembly (MEA) is expected to be a breakthrough for the CO₂ electroreduction. Particularly, methanation (converting CO₂ into CH₄) with MEAs incorporating Cu-based catalysts attracts special attention as a tool for carbon cycling, thanks to high faradaic efficiencies and relatively high energy conversion efficiencies. Different from Cu, Pt has long been recognized as an inactive catalyst for CO₂ reduction. Contrary to the common consensus, MEAs incorporating a Pt-based electrocatalyst were found very recently to be as active as Cu-based catalysts toward methanation under specific reaction conditions. The high activity of Pt arises from a reaction mechanism different from that for Cu; most likely the Langmuir–Hinshelwood mechanism for Pt and the Eley–Rideal mechanism for Cu. This mini-review discusses CO₂ electrochemical methanation using MEAs as a potential method for carbon capture. The CO₂ reduction to CH₄ using a H₂-CO₂ fuel cell is also presented.

Graphical Abstract